The routing in a conventional multicast is realized by a dedicated protocol for the multicast. In this dedicated protocol, when a connection request is received from a client terminal, it is necessary to set up a network, which is managed in a tree structure, for each additional connection. Accordingly, there is a problem that the operational efficiency is low. In addition, in this case, there are problems that, precisely, it is difficult to generate a distribution tree, and that it is also difficult to carry out distribution for each source type. Further, it is difficult to provide a multicast service, and thus to conveniently use the multicast service on-demand.
Incidentally, for example, JP-A-2004-172819 discloses a technique capable of carrying out simple transmission, transmission by an explicit path, and transmission whose bandwidth is ensured, in multicast data transmission. More specifically, while a transmission route is formed by a multicast protocol, a transmission route formation manager operates as follows. That is, a label is assigned to a relay device and is included in a participation message to form LSP. Next, a required bandwidth is ensured in a policy table, and is then entered into the participation message. Then, the explicit addresses of the relay devices on the transmission route are designated in the policy table, and the explicit transmission route is formed by the addresses.
In addition, JP-A-2004-32114 discloses a technique in which, under a large-scale MPLS network environment, multicast path settings for a source activation and a leaf activation are possible, two setting mechanisms can be mutually operated without inconsistency there between, QoS can be ensured, and the addition, removal or correction of a necessary partial tree can be carried out, without resetting the entire multicast LSP which has already been set. Specifically, in addition to a path setting function by the source activation, the technique includes a participation function into the multicast tree by the leaf activation, a function for designating a path setting node by the leaf activation, a function for selecting a branch point by the leaf activation, a function for grafting and pruning the tree by the source activation, a mutual operation function of the source and leaf activations by specifying a path by a multicast session identifier, a function for allocating plural traffics to one LSP, a function for setting and releasing a path between multipoints, a function for explicitly specifying a transferring path, and other functions.
As described above, various multicast transmission techniques have been disclosed. However, a technique using a Reverse Label switched Path (RLP) in a Multi-Protocol Label Switching (MPLS) network has not been disclosed, yet. In addition, because RSVP (Resource reSerVation Protocol) or a protocol equivalent thereto is used, the processing load increases. Furthermore, because the configuration of the multicast tree should be updated for each occurrence of the participation, the processing load increases.